Force transmission linkage for automotive vehicles

ABSTRACT

A force transmission linkage for an automotive vehicle couples a control member with a manoeuvring member of a declutching device for a clutch, and is of the kind comprising a mechanical part with application points carried by a fixed part of the vehicle. 
     In accordance with the invention, one of the said application points of the linkage is movable under the action of a control device comprising a motor and a transmission acting between the said motor and the said movable application point. A sensor for detecting a supplementary strain in the linkage, is provided together with a computer, with the computer receiving information signals from the strain sensor for control of the motor.

FIELD OF THE INVENTION

The present invention relates to linkages for transmitting forces inautomotive vehicles, such a linkage being adapted to couple a controlmember with a manoeuvring member of a declutching device for a clutchand being of the kind including a mechanical part.

BACKGROUND OF THE INVENTION

Reference is here made to FIGS. 1 to 4 of the accompanying drawings.What these Figures represent is explained in the section "BriefDescription of the Drawings" which appears further on in this document,and to which reference is invited at this point.

Referring to FIGS. 1 and 2, the linkage commonly comprises a cable 1which is movable axially, a sheath 2 surrounding this cable, and a fork4 which is pivotally mounted about a pivot or articulation point 7,which may for example consist of a knuckle piece secured to a fixed partof the vehicle as shown in FIG. 2, or a spindle which is rotatable andwhich is carried by a fixed part of the vehicle. In a variant, thearticulation point may consist of bearings, with the fork then carryingprojections which are rotatable in the said bearings, the latter beingfor example mounted in the gearbox casing.

Generally speaking the articulation point 7 constitutes a guide or datumpoint for the linkage.

The manoeuvring member is a clutch release bearing 3 which is subjectedto the action of the declutching fork 4, and which is adapted to act onthe declutching device of a clutch such as the ends of the fingers of adiaphragm 6 or declutching levers. The control member 8 most oftenconsists of a pedal pivotally mounted about a pivot point 9, which isagain fixed with respect to a fixed part of the vehicle.

The cable 1 is attached at each of its ends 10 and 11 to attachmentpoints at which it is attached to the pedal 8 and the fork 4respectively, while the sheath 2 is interposed between two points 12 and13 that are fixed with respect to the vehicle.

The pivot points together with the fixed points will together bereferred to in this document as "application points" for the linkage,which may include an hydraulic part, for example between the fork 4 andthe clutch release bearing 3. These application points have theessential feature that they are ultimately carried by a fixed part ofthe vehicle, being secured to such fixed part or mounted rotatably withrespect to it.

It is not obligatory to provide the fork 4, in which connection thepoint 11 may be attached to a disc in the manner described in Frenchpublished patent application No. FR 1 587 732A; alternatively, it may beattached to a driving member in the manner described in U.S. Pat. No.4,934,503 and the corresponding published European patent applicationNo. EP 0 322 265A.

In FIG. 1, when the pedal 8 is depressed, this exerts a pulling force onthe cable 1 which, guided by the sheath 2, actuates the fork 4.

Referring to FIG. 3, the point 11 may of course be fixed while the point13 can be movable by virtue of being attached to the fork 4, so thatwhen the position of the point 10 is varied, this involves acorresponding variation in the position of the point 13. In a modifiedembodiment, see FIG. 4, the points 10 and 11 may be fixed and the points12 and 13 may be movable, being attached respectively to the pedal 8 andto the fork 4. The cable 1 then serves to guide the sheath 2 which isthen axially movable. In all cases, one of the elements consisting ofthe cable and its sheath is a force transmitting element, while theother one of these two elements is a guide element.

In a further variant, the linkage can include a force transmittingelement which is in several parts, having a plurality of bars with areturn system and at least one articulation point carried by a fixedpart of the vehicle, this articulation point then constituting a guideor datum point for the linkage.

In practice, the course of travel of the control member 8 and themanoeuvring member 3 can be broken down into a dead stage, a modulatingstage with sliding movement, and a final stage to give complete couplingby the clutch. For example, and referring to FIG. 2, in the case of aconventional friction disc clutch 16, the dead stage occurs between thedeclutching position, in which the friction disc is free, and anintermediate position, referred to here as a take-up position, in whichthe friction liners 16' of the clutch disc 16 come into light contactwith the pressure plate 15 of the clutch. The modulating stage occurswith circumferential sliding movement of the friction liners 16' betweenthe reaction plate 17 and the pressure plate 15 of the clutch, and withan increasing amount of torque being transmitted until coupling iscomplete at a position referred to as the coupling position. The finalstage enables good coupling to be achieved between the driving shaft Mand the driven shaft B of the clutch. The driving shaft M is secured tothe engine of the vehicle, for rotation therewith, and the driven shaftB is the input shaft of the gearbox. The modulating stage is thusvaluable for passenger comfort and in facilitating manoeuvring of thevehicle, while the dead stage is necessary having regard tomanufacturing tolerances of the various components of clutch, and alsohaving regard to distortion effects, in particular the tendency of thepressure plate 15 to assume a slightly conical shape due to thermallyinduced forces to which it is subjected.

It should be mentioned here that the pressure plate 15 is rotatable witha cover plate 14, being movable axially with respect to the latter. Thiscover plate 14 is adapted to be carried on the reaction plate 17, whilethe diaphragm 6 bears on the cover plate 14 for action on the pressureplate 15 and for urging the latter towards the reaction plate 17, sothat the friction pads 16' are gripped between the pressure plate 15 andthe reaction plate 17. The plate 17 is secured to the engine or drivingshaft M, while the clutch disc 16 is secured to, and rotatable with, thesecondary or driven shaft B.

As the friction pads 16' become progressively worn, their thicknessvaries in such a way that the diaphragm 6 becomes inclined so as todisplace the clutch release bearing 3. The latter then acts on the forkto exert an indirect pull on the cable 1. If no particular position istaken up, then with a constant linkage length, the result is seenparticularly in the undue appearance of a clearance which causesuncontrolled slipping on the friction pads 16'. This is detrimental tothe useful life of the clutch.

In order to overcome these drawbacks, it has already been proposed, inU.S. Pat. No. 4,304,322 and the corresponding French published patentapplication No. FR 2 420 164A, to divide the cable of the linkage intotwo successive pieces, the first of which is coupled with thedeclutching fork and the second piece being coupled to the controlpedal. A compensating device is also provided, with the lattercomprising two coupling members which are telescopically movable axiallywith respect to each other, and each of which is adapted to be coupledin movement to a respective one of the two parts of the cable incooperation with disengageable locking means which are adapted toconnect the said coupling members temporarily with each other, in onlyone axial direction of action of the latter.

Such an arrangement thus requires the cable to be cut in two and isitself subject to wear, because the disengageable locking means operatesevery time the driver operates the control member.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel linkage which,incorporating a mechanical part which is actuated manually by thedriver, allows the length of the linkage to be modified in a simple andeconomic manner with minimisation of wear and also with otheradvantages.

In accordance with the invention, a linkage of the type defined above ischaracterised in that one of the said application points of the linkageis movable directly or indirectly under the action of control meanswhich comprise motor means and a transmission operatively connectedbetween the said motor means and the said movable application point; inthat at least one sensor for detecting a supplementary strain in thelinkage is provided; and in that a computer is provided, with the saidcomputer receiving information signals from the said supplementarystrain detection sensor whereby to control the said motor means, so thatthe said sensor transmits a signal to the computer when a said strain ispresent, whereby the computer causes the said motor means to operate soas to displace the movable application point, thereby taking up wear.

The invention enables wear to be taken up at specific times, for examplewhenever the engine is stopped or reverse gear is engaged. It will ofcourse be appreciated that the force transmission element does not needto be divided into two parts.

All of the foregoing allows wear to be minimised.

The movable application point may be indirectly movable: and in thiscase either the sheath or the cable can be cut, depending on thearrangement adopted, with the point of the cut itself being displaced.It must however be emphasised that in every case the component that isdivided into two parts is that which serves only as a guiding elementand not the one that transmits force.

It will be understood that the defined course of travel of the movablemember is thus developed in an evolutionary manner according to theprogress of wear of the friction pads, and that the linkage inaccordance with the invention can be fitted in place of a conventionallinkage while preserving the maximum possible number of components ofthe latter. It will also be understood that the control means aresimplified as compared with an automatic type of linkage such as thatdescribed in French published patent application No. FR 2 564 920A.

In accordance with a preferred feature of the invention, the linkagefurther includes a sensor for detecting the free position of the controlmember (this free position corresponding to an absence of any action bythe driver on the control member such as a clutch pedal), in such a waythat the adjustment for compensation for wear takes place only when thesaid control member is in its free position.

Due to the computer, it is of course possible to choose other criteriaas to when action to compensate for wear will take place, for exampleonly when reverse gear is selected. In this case a sensor is associatedwith the gear change lever so that it transmits a command signal for thewear compensation procedure only when the gear lever is in its reverseposition.

The motor means may be permanently energised: however, the control meansare preferably made irreversible, in such a way that the motor means donot need to be energised permanently, and also so that the movableapplication point remains fixed when the driver operates the controlmember at times other than those at which the wear compensationadjustment is to be carried out.

In accordance with a further feature of the invention, it is possible touse the motor means to assist the performance of the dead stage of thecourse of travel, while giving the driver the opportunity to effect themodulating stage manually. To this end, at least one first positionsensor is preferably associated with the control member, and a secondposition sensor with the movable application point. The computerreceives information signals from the said position sensors in order tocontrol the said motor means, so that by actuation or release of thecontrol member by the driver, and thus by the resulting action of thecontrol member on its associated position sensor, the driver commandsthe starting of the motor means so as to displace the said movableapplication point in a first direction or in a second direction. Thisdisplacement takes place in accordance with the action exerted by thedriver on the control member, up to a terminal position of the course oftravel detected by the position sensor associated with the movableapplication point, the said movable application point being then fixedby means of the control means when the driver actuates the controlmember manually.

It will further be appreciated that the invention enables twocontradictory requirements to be reconciled, for a substantiallyconstant course of travel of the control member: namely to increase themodulation stage without reducing the dead stage. It will also beappreciated that the application point concerned is movable in bothdirections along a course of travel defined between two limit positions.

In accordance with a major feature of the invention, a sensor isprovided which detects the free position of the control member, togetherwith sensors which are arranged to detect slipping movement of thefriction disc and/or predetermined rotational velocity. This makes itpossible to arrange for the motor means to act in such a way as to causethe friction disc to slip without the driver having to intervene usingthe pedal. Controlled slipping is thus obtained, such as to enable, inparticular, momentary overtorques from the engine to be absorbed, whichimproves the useful life of the transmission components, reduces noiseand avoids clutch snatch, to the benefit of the comfort of the occupantsof the vehicle.

The present invention thus enables both the final stage and themodulation stage of the course of travel, or either of them, to bemodulated by means of the motor means.

The features and advantages of the invention will appear from thedescription of preferred embodiments of the invention which is givenbelow, by way of example only and with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an actuating linkage of the prior art,in a first embodiment.

FIG. 2 is a diagrammatic view showing a friction clutch associated withthe linkage of FIG. 1.

FIGS. 3 and 4 are views similar to FIG. 1, showing respectively twofurther embodiments.

FIG. 5 is a diagrammatic view of the linkage, similar to FIG. 1 butshowing a first embodiment of the present invention.

FIGS. 6 to 10 are views similar to FIG. 5, showing further embodimentsof the invention, but with the computer being omitted from FIGS. 6 to 9.

FIG. 11 is a front view of the motor means with their associatedirreversible transmission, in a first embodiment.

FIG. 12 is a view in cross section, taken on the line 1--1 in FIG. 11,but with the electric motor not shown in cross section.

FIGS. 13 and 14 are views similar to FIGS. 11 and 12 but showing asecond embodiment, FIG. 14 being a view in cross section taken on theline 2--2 in FIG. 13.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In FIGS. 5 to 14, those elements that are identical to those describedabove with reference to FIGS. 1 to 4 are designated by the samereference numerals, the application points (this term having the meaningexplained earlier herein) being points ultimately carried by a fixedpart of the automotive vehicle and the latter having an internalcombustion engine.

Referring to FIG. 5, the linkage includes an application point 13 whichis directly movable with respect to its fixed vehicle support in bothdirections in a course of travel which is defined between two limitpositions and under the action of control means 200, which include motormeans 20 and a transmission 30 interposed between the motor means 20 andthe application point 13. Position sensors 50 and 60 are associatedrespectively with the control member 8 and with the movable applicationpoint 13. A computer 40 is provided for receiving the informationsignals supplied by the position sensors 50 and 60 and for controllingthe motor means 20 in response to this information. On depression orrelease of the control member 8 by the driver, with resulting action bythe control member 8 on its associated position sensor 50, the computer40 energises the motor means 20 so as to displace the movableapplication point in a first direction or in a second direction, inaccordance with the action exerted by the driver on the control member 8up to a terminal position at the end of the course of travel. Thisterminal position is detected by the position sensor 60 associated withthe movable application point 13. Under the action of the control member8, when the position sensor 50 associated with it does not give a signalwhich is capable, via the computer 40, of energising the motor means 20,the control means 200 keep the movable application point 13 in a fixedposition.

A sensor 80, for detecting any supplementary strain that may be presentin the linkage, is provided in association with the movable applicationpoint and the computer. The computer receives signals from thesupplementary strain detecting sensor 80, so as to control the motormeans 20 in such a way that the sensor 80 delivers a signal to thecomputer 40 when a supplementary strain is present, to enable thecomputer to energise the motor means 20 in such a way as to displace themovable application point, thus taking up any wear.

The motor means 20 and the transmission 30 thus form part of a controlsystem which is driven by driving means comprising the computer 40 andthe sensor 80 which provides the means for detection. The motor means 20may be permanently supplied with power and can hold the movable point 13in a fixed position regardless of any compensation for wear: however,the control means 200 are preferably made irreversible. In FIG. 5, thetransmission 30 is irreversible, as it is in FIGS. 12 to 14 which are tobe described below.

The sensor 80 is associated with the point 11 (see also FIG. 12), and itis the application point 13 associated with one end of the sheath 2 thatis movable. The position sensor 50 associated with the pedal 8 is in theform of a switch for detecting the end of the travel of the pedal, whilethe sensor 60 which is associated with the movable application point 13is in the form of a potentiometer, the mid point of which is connectedto the computer 40. The computer 40 has supply inputs C and D, togetherwith signal inputs for receiving signals E, F, and G respectively. Thesignals E and F are delivered by sensors 101 and 102 (FIG. 2). Thesignals E, F and G represent, respectively: the rotational velocity ofthe reaction plate 17 of the clutch, and therefore that of the drivingshaft M; the rotational velocity of the secondary or driven shaft B; anda parameter which is related to the acceleration of the vehicle, such asthe position of the butterfly valve of the carburettor or the positionof the accelerator pedal. The computer 40 receives the signals from thesensors 50 and 60 as well as that from a further sensor 51 which detectsthe free position of the pedal 8, i.e. it detects when the driver's footis not on the pedal. The sensor 51 is, in the arrangement shown in FIG.5, a switch or interruptor.

Thus, when the driver operates the pedal 8 with his foot, so that theswitch 50 is not operated by the pedal 8, the clutch torque can bemodulated manually, with the friction disc 16 of the clutch then goingprogressively from the engaged state to the disengaged state and viceversa.

When the driver pushes the clutch pedal 8 hard down, this operates theswitch 50 (indicating that the clutch pedal has been operated), and thecomputer 40 receives the appropriate signal and triggers energisation ofthe motor means 20. The latter then cause the movable application point13 to be displaced in a first direction, up to a first extreme positionwhich is set by the potentiometer 60, so as to effect the dead stage ofthe course of travel of the clutch in a first direction.

When the driver then releases pressure on the pedal, the latter returnsto its free position, and the switch 50 therefore reverts to its initialmode. In response to this, the computer energises the motor means 20 inthe opposite direction, so that the movable application point 13 isdisplaced in the opposite direction up to a second extreme position,which is again set by the potentiometer 60. It will thus be seen thatthe application point 13 is movable in both directions along a definedcourse of travel between two extreme limit positions which aredetermined by the potentiometer 60.

When the pedal is in the relieved or free position, the sensor 51transmits a signal to the computer 40, such that the latter willenergise the motor means 20 when, through its input G from an associatedsensor that detects a variation in the acceleration of the vehicle (suchas a sensor responsive to the position of the carburettor butterflyvalve or an accelerometer), it will detect major variations inacceleration (for example), so as to disengage and engage the clutch.This has the particular result of improving the comfort of the occupantsof the vehicle. The sensors which transmit the signals E and F make itpossible to arrange for the clutch to change its mode smoothly, inaccordance with a characteristic curve determined in advance, over apredetermined range of its travel, thus reducing noise and shock.

When the pedal 8 is free, a supplementary traction force, or pull, isdetected by the sensor 80, which transmits a signal to the computer 40.The latter accordingly energises the motor means 20 until no residualforce exists. This action compensates for the effects of wear.

It will be noted that this supplementary pull is due to the frictionpads 16', which, as they wear, cause changes to take place in theinclination of the diaphragm 6 and of the fork 4 which pulls on thecable 1. It will also be appreciated that the force transmission cable 1is not cut. The same is true in FIG. 6, in which it is the end point 11of the cable 1 that is movable; and again in FIG. 7. In FIG. 6, a straingauge 180 is associated with the sheath 2, to detect any modification inthe strain on the latter. The strain gauge 180 is shown in FIG. 6associated with the application point 12, while in FIG. 7 the straingauge or sensor 80 is shown associated with the application point 13.

Generally speaking, however, rather than using a strain gauge, it ispreferred to use a sensor which is of the kind comprising adeflection-responsive switch that is held in one of its positions by areturn spring or, in a modification, by a piece of elastomeric materialthat includes the contact strips, with the contact strips completing acircuit when the elastomeric element is deformed by more than a certainamount. Thus the switch is closed in direct response to the deformationbeing sensed.

Referring now to FIG. 8, the guide sheath 2 is divided into two piecesbetween the two fixed application points 12 and 13, and it is the pointat which the sheath is divided that is movable, given that a deformationof the sheath 2 causes the relative position of the points 10 and 11 tovary. This arrangement results in indirect displacement of the movablepoints 12 and 13, since mobility of the point at which the sheath isdivided causes the relative positions of the points 10 and 11 to vary inthe same way as in FIG. 5, the only difference being that the guidesheath 2 is cut. In this case, the supplementary strain detectionsensor, 280, is associated with the point 11 like the sensor 80 in FIG.5.

It will be appreciated that it is the component which acts as a guidethat is divided into two pieces, with the associated element, i.e.either the cable 1 or the sheath 2 as the case may be, of the forcetransmission means remaining intact.

The housing of the motor means 20 is of course connected resiliently,for example by means of a spring 28, to a fixed part of the vehicle inorder to enable it to adapt to the movements of the sheath 2. Thishousing also preferably contains the irreversible transmission. In thisway the control means 200 can be made as a single unit.

Referring now to FIG. 9, the wear effect sensor, here denoted by thereference numeral 380, is associated with the application point 11, andthe linkage comprises a train of rods 71, 72, 73 with respective pivotpoints 74, 75, 76 between the ends 10 and 11 of the train of barsconstituting the linkage. The pivot point 75 is ultimately secured to afixed part of the vehicle and constitutes the datum or guide point forthe linkage, the latter being movable. The force transmission element isthus in several parts in this case, namely the rods 71 to 73.

Reference is now made to FIG. 10, in which the pivot point 7 of the fork4 constitutes the datum point for the linkage. In this case the linkageis movable. It will be noted that in FIG. 10, the two sensors 50 and 51have been replaced by a potentiometer 52 which detects the free positionand the depressed position of the pedal 8. It will also be noted thatthe wear effect sensor, here denoted by the reference numeral 480, isassociated with the application point 10, and detects the pull on thecable as the friction pads 16' become worn. This sensor 480, disposedwithin the linkage, detects whether or not there is an internal force inthe linkage.

In the embodiment shown in FIGS. 11 and 12, to which reference is nowdirected, it can be seen that the sensor 80 is interposed between theupper end of the fork 4 and a fastening screw for the cable 1. It can ofcourse detect a force exerted on the sheath, when associated with thepoint 12 or 13.

It will be recalled that, as the friction pads 16' become worn, thethickness of the latter varies in such a way that the diaphragm 6, whichin the example shown in FIG. 2 is mounted pivotally on the cover plate14 with the clutch release bearing 3 acting in thrust, becomes inclinedand displaces the clutch release bearing 3, which pulls indirectly onthe cable 1 by acting on the fork 4. The pedal is normally biassed intoits free position by a spring. When the pedal is free it is the abovementioned pulling force that is detected by the sensor 80, and thelatter transmits a signal to the computer 40, which energises the motormeans 20, as explained above, until a zero residual force is obtained.The computer can be programmed so that it will carry out this operationunder predetermined situations, for example whenever the engine of thevehicle is started or stopped. It should be noted that the free positionof the pedal is that in which it is not being operated by the driver.

In the embodiment shown in FIGS. 11 and 12, the motor means comprise anelectric motor, while the transmission includes intermediate worm wheels31 and 32 which mesh with a worm 21. The latter is driven by theelectric motor 20, the arrangement being similar to that described inFrench published patent application No. FR 2 372 998A. The worm 21 is intwo portions having different pitches, each of these portions meshingwith a respective one of the worm wheels 31, 32. Each of the latter isof the double type, and includes a part which is adapted to mesh with arack 34 formed on a sliding member 33.

The electric motor 20, together with the irreversible transmission 30which comprises the worm 21 with its two worm wheels 31 and 32 meshingwith the rack 34, is housed in a common housing 22, with the slidingmember 33 being movable longitudinally in a bore 37 of the housing 22,in which guide rings 36 are mounted.

The cable 1 extends into the interior of the sliding member 33. At oneof its axial ends, the latter has a shouldered plug 81, having agenerally U-shaped cross section, with radial ends defining a shoulderfor engagement on the housing 22. This plug 81 receives the end of thesheath 2, and is secured to the sliding member 32, for example by meansof a force fit. In a modification, it may be made integral with thesliding member. It will be noted that the sliding member 33 is formedwith a flattened portion 35 to accommodate the worm wheels 31 and 33.

The axis of the worm wheel 32 is extended, as indicated at 61, in orderto drive an arm 62, which is the cursor of the potentiometer 60. Thislatter is mounted within a casing 63 secured to the housing 22. Thus,when the electric motor 20 is driven, the worm 21 rotates in onedirection and drives the worm wheels 31 and 32, which displace the rack34 and therefore the plug 81 and the sheath 2, until the arm 62 reachesan end position. Movement in the opposite direction is then possiblefrom this position, until the arm 62 reaches the second extreme positionof the potentiometer 60. In this embodiment, it is the application point13 that is thus movable.

It will be noted that, when the pedal 8 pulls on the cable, the sheath 2cannot also be pulled, because of the irreversibility of thetransmission 30 and the fact that the motor 20 is not energised. Bycontrast, the sliding member 33 is able to be displaced in bothdirections by the electric motor 20.

The curvature of the sheath 2 is able to be varied by displacement ofthe movable application point, so that the fork 4 is caused to pivot,with the potentiometer 60 then detecting the end of the travel of theapplication point 13. The effect of this is that a signal is transmittedto the computer 40, which stops the electric motor 20. The latter isthen not supplied with further power. On reengagement of the clutch, thepotentiometer permits the movable application point 13 to revert to itsinitial position, so as to enable the modulation stage to be carried outby the driver of the vehicle. The position of termination andcommencement of the course of travel is memorised by the computer 40 oneach occasion when wear is taken up, so as to displace, in successiveevolution, the limit positions of the movable application point 13.

Reference is now made to FIGS. 13 and 14, in which the motor means 20are again in the form of an electric motor. However, in this embodimentthe irreversible transmission, here denoted by the reference numeral300, does not have the rack 34 or sliding member 33. Instead, it has atoothed sector 90, which meshes with the worm wheels 31 and 32 and whichis mounted about a pivot point 92 that is fixed with respect to thefixed housing 22. On rotation of the worm wheels 31 and 32, the sector90 undergoes pivoting movement so as to displace the application point13. The latter is carried on the lower end of the sector 90 by means ofa ring-type fastening 91.

As will be clear from the foregoing, the motor means 20 and theirreversible transmission 30 or 300 associated with it constitutecontrol means which act on the linkage, while the computer 40 and thevarious sensors 50, 60 or 51, 52, 80 constitute driving means for thesaid control means.

The sensor 80 may be associated with the guide element of the linkage;however, it is preferably associated with an application point of theforce transmission element or with a pivot and guiding point, while themovable application point is associated with the guide element or with apivot and guiding point. In the interests of precision, the sensor 80 ispreferably associated with the force transmission element.

The present invention is of course not limited to the embodimentsdescribed above, but embraces all variants within the broad scope of theclaims. In particular, the motor means may be of an hydraulic type, withthe computer 40 then controlling an electric pump which varies thepressure in a chamber which is defined by a cylinder and a piston, so asto displace the piston and thus a movable application point of thelinkage.

Similarly, the irreversible transmission may include an electric motorhaving a worm or lead screw meshing with a reduction gearing includingpinions, one of the pinions of the meshing means including a spiralgroove, into which a finger or lug penetrates. This finger or lug isfixed with respect to one end of a pivoting lever, the other end ofwhich also has a finger which is in engagement with the screw thread ofa movable member mounted in a bore formed in the housing. Then, when themotor is in rotation, the lever is caused to pivot so as to drive themovable member in displacement, with the latter carrying one of theapplication points of the linkage, for example one end of the sheath 2.The cable 1 passes through the said movable member.

The motor means 20 may themselves be irreversible, by a suitablearrangement of the magnetic fields, for instance; alternatively,irreversibility of the motor means may be achieved by the use of abrake, arranged to act for example on the output shaft of the motor.

As mentioned above, it is of course not obligatory to provide thelinkage with a fork, and the linkage may include an hydraulic part. Forexample, in FIG. 9, the application point 11 may be connected to a discwhich is rotatably mounted on a fixed part of the vehicle, with thisdisc being part of a system comprising a crank and connecting rod, thecrank being coupled to the piston of an output cylinder, the latterbeing connected through suitable ducting to an input cylinder whichactuates the declutching fork.

The control member of the linkage may be in the form of a lever orhandle, for example for a power drive under the control of the driver ofthe vehicle.

The application points 10 and 12 may be made movable. For example, inFIG. 5 the application point 12 may be displaced instead of theapplication point 13, while in FIG. 7 the point 10 may be displaceableinstead of the point 11.

The potentiometer 60 may be replaced by two switches, comprisingrespectively a switch corresponding to the commencement of the course oftravel, and one corresponding to the termination of the course.

The electric motor may be arranged to rotate in only one direction, andits output shaft or axis 21 may be coupled mechanically through anirreversible reduction gear, comprising a plurality of pinions, to adriving element cooperating with a transverse pin-type element carriedby a sliding member. The driving element then comprises two peripheralprojections, substantially in the form of helical sections, which areinclined in opposite directions with respect to the axis of the drivingelement, with these peripheral projections also being offset axially andangularly from each other.

In FIGS. 6 and 7, it is for example possible to make the applicationpoint 11 (or the point 10) indirectly movable, by cutting the cable 1 intwo and by displacing the point at which the cable is cut in a mannersimilar to that described above with reference to FIG. 8 and inconnection with the sheath 2, given that in every case only one of theelements comprising the cable 1 and sheath 2 is cut (namely that whichconstitutes the guide element), with the housing 22 being resilientlysuspended as in FIG. 8.

Finally, instead of the wear compensation adjustment being carried outin the free position of the pedal, different criteria may be applied:for example, there may be a sensor associated with the gear change leverfor detecting the position of that lever for engaging reverse gear. Anappropriate signal is then transmitted to the computer 40 for wear thento be taken up in this position. Preferably, advantage is taken of thesensor which is usually present in the vehicle for switching on thereversing lights when the driver engages reverse gear.

The presence of the sensor which is associated with the movableapplication point is not obligatory. If it is omitted, the computer maybe programmed in such a way as to generate a signal representing theposition for the motor means in response to a control signal produced bythe sensor which is associated with the control member (e.g. the pedal),in such a way as to displace the movable application point from one ofits limit positions to the other.

For example the motor means may comprise an electric motor of thestepping type, for displacing the movable application point from one endposition corresponding to one of its limit positions, to another endposition corresponding to its other limit position. This progressionwill take place in response to a limited number of command pulses ofpredetermined duration, generated by the computer in response to thecontrol signal from the associated sensor. Memorisation of the endpositions will then take account of actual wear, in particular wear ofthe friction pads or liners of the clutch, so that the command pulsesare evolved as a function of actual wear.

In every case, a course of travel of the movable application pointinvolves movement of the manoeuvring member.

Finally, the driver can carry out part of the dead stage of the courseof travel manually, but with the major part of the dead stage beingeffected by the control means.

What is claimed is:
 1. An operating mechanism for the clutch of anautomotive vehicle having a fixed part, its clutch comprising a pressureplate, a reaction plate, a friction disc between the pressure plate andthe reaction plate, and means for causing the friction disc to begripped by the two plates, wherein the clutch operating mechanismcomprises a declutching device which is associated with the clutch andwhich includes a manoeuvreing member, the mechanism further comprising acontrol member, operable by the driver of the vehicle, and a forcetransmission linkage coupling said control member with said manoeuvreingmember, said linkage comprising a mechanical part including a forcetransmission element in at least one piece, the mechanical part alsoincluding means defining a plurality of application points carried bysaid fixed part of the vehicle, the linkage further comprising controlmeans, and said control means comprising a motor means and atransmission means coupled with the motor means to be driven thereby,one of said application points being connected through said transmissionmeans to said fixed part to be movable with respect to said fixed partby said transmission means, wherein the linkage further includes asupplementary strain detection sensor for detecting a supplementarystrain in the linkage, the mechanism further including a computerconnected with the said supplementary strain detection sensor and withthe said motor means and position sensor or sensors, whereby to receiveinformation signals from the said supplementary strain detection sensorto control the said motor means, whereby on receipt of a signal from thesupplementary strain detection sensor when a supplementary strain ispresent, the computer causes the said motor means to operate so as todisplace the movable application point in a sense such as to take upwear in the clutch.
 2. A mechanism according to claim 1, furthercomprising a position sensor associated with the control member forsensing a free position of the latter, the computer being connected withsaid position sensor so that the position sensor transmits a signal tothe computer so that computer then causes the said motor means tooperate in response to the information signal received from saidsupplementary strain detection sensor.
 3. A mechanism according to claim2, wherein, the clutch being coupled to a driving shaft and a drivenshaft, the mechanism further includes speed sensors for detecting therotational velocity of the driving shaft and driven shaft respectively,whereby in said free position of the control member, the associatedposition sensor transmits a signal to the computer, so that the computerthen actuates said motor means in accordance with a pre-establishedcharacteristic in response to signals from said speed sensors.
 4. Amechanism according to claim 1, having at least one first positionsensor, being a said position sensor associated with the control member,and a second position sensor associated with said movable applicationpoint, the computer being connected with said first and second positionsensors whereby, when said control member is actuated or released by thedriver so that the control member acts on at least one said firstposition sensor, the computer causes the motor means to drive thetransmission means so as to displace the movable application point withrespect to said fixed part, in a direction selected from a firstdirection and a second direction according to the action exerted by thedriver on said control member, up to a terminal position in its courseof travel, the second position sensor being arranged for detecting saidterminal position, and whereby the movable application point is fixedwith respect to said fixed part by said control means on manualactuation of said control member by the driver.
 5. A mechanism accordingto claim 1, wherein said control means are irreversible.
 6. A mechanismaccording to claim 5, wherein:said motor means comprises an electricmotor and a worm driven by the electric motor; and , said transmissionmeans includes worm wheels meshing with said worm.
 7. A mechanismaccording to claim 6, further comprising:a housing for said motor meansand said transmission means, said housing defining a bore therein, asliding member mounted in said bore for sliding movement therein alongan axis with respect to the housing, and a rack formed on the slidingmember and meshing with said worm wheels; said force transmissionelement comprising a cable and surrounding sheath, an end of said sheathcomprising said movable application point and being associated with andmoved by said sliding member.
 8. A mechanism according to claim 6,further comprising:a housing for said motor means and said transmissionmeans; and, a toothed sector pivotally mounted with respect to the saidhousing, said toothed sector having a toothed portion, meshing with thesaid worm wheels, and another portion engaging and moving said movableapplication point by pivoting motion of said toothed sector with respectto said housing.